This invention relates to an isokinetic air sampler. The invention also relates to a system for taking air samples isokinetically so that the airborne concentration of particulate pollutants can be accurately measured. The invention further relates to a method of sampling air isokinetically to measure airborne concentration of particulate pollutants as a function of wind speed.
Air sampling systems capable of monitoring the atmosphere to determine the extent of pollution by particle emission and to determine how effective antipollution control devices are are well known. Such devices normally use a filter to collect the particles employing an air pump to draw air through the filter. If the air pump is turned on at all times, it is not possible to obtain samples representative of conditions at any particular wind speed; if the air pump is turned on only when the wind speed is at the desired value, air impact pressure will force some air through the filter and cause some particle collection when the air pump is turned off. In addition sampling will not necessarily be isokinetic; i.e., introduced into the sampling system without substantial perturbations of the kinetics of the gas being sampled. If the flow of air around the sampler is at a different speed from the flow of air into the sampler, the sample may not accurately reflect the air being sampled because of the inertia of the particles approaching the sampler.
Monitors have long been known which collect or sample particulate matter from stack gas or any gas flowing through a conduit and isokinetic samplers and techniques for this purpose are well known. The wide variations observed with respect to wind speed, however, do not normally apply to a stack or conduit. Thus samplers and sampling techniques used for air sampling have not heretofore been accurate enough to measure airborne concentrations of particulate pollution as a function of wind speed.